Laser recording method

ABSTRACT

A novel electrophotographic imaging system employing persistent conductivity materials is disclosed. Laser radiation is utilized with subsequent charging and developing to provide sharp clear reproductions of an original. A two color process employing one developer is also disclosed.

United States Patent Tamai et a1.

1 1 Sept. 30, 1975 1 LASER RECORDING METHOD [75] Inventors: Yasuo Tamai; Masaaki Takimoto;

Akira Nahara, all of Tokyo, Japan; Masamichi Sato, Tucson, Ariz. [73] Assignee: Rank Xerox Ltd., London. England [22] Filed: Mar. 19, 1973 [211 App]. No.: 342,634

[30] Foreign Application Priority Data Dec. 28. 1970 Japan 45-120326 [52] US. Cl. 96/1 R; 96/1.8 [51] Int. Cl. G03G 5/08 [58] Field of Search 96/27 H. 1.1, 1; 346/76; 331/945; 250/65 [56] References Cited UNITED STATES PATENTS 2.845.348 7/1958 Kallmann 96/1 R Primary ExaminerNorman G. Torchin Assistant E.\'aminer.lohn L. Goodrow 9 Claims, N0 Drawings LASER RECORDING METi-ion BACKGROUND OF THE INVENTION This invention relates to electrophotographic imaging and more specifically to electrophotographie imaging processes employing lasar recording techniques.

In the conventional electrophotographic imaging process commonly referred to as xerography a photoconductive member is charged selectively illuminated and then developed to provide a reproduction of an original. A suitable photoconductor, for example selenium, exposed either on a plate or ordinarily as commercially employed on a revolving drum is charged to a voltage of, for example +1000 volts then selectively illuminated by slit-scanning of an original to provide a latent electrostatic image of the original. The latent electrostatic image is then rendered visible by activating a development mechanism for example, a cascade development system, which deposits electroscopic marking material commonly referred to in the art as toner on the latent electrostatic image thereby rendering it visible. In the case where the toner is the same charge as the image, development occurs in non-image areas and in the case where the toner possesses a charge opposite to that of the electrostatic latent image development of image areas is achieved. The image so produced may then be transferred if desired and then fixed or fixed in situ to provide a permanent reproduction of the original. Fixing is conventionally accomplished by application of heat such as for example a fuser roll or may be accomplished by application of a suitable solvent.

Some electrophotographic imaging materials after exposure to actinic radiation retain the conductivity in the light-struck areas for a brief to long periods of time and are referred to in the art as persistent conductivity materials. Typically these materials may be employed as follows: the material is first selectively exposed and then electrostatically charged after a suitable period of time resulting in the formation of a latent electrostatic image after which the image is developed employing conventional techniques. Depending on the material used the persistent conductivity effect realized sometimes referred to as fatigue of the photoconductor, may endure for a very short to a substantially longer period of time thereby requiring either immediate subsequent charging or allowing storage of the exposed member for substantial periods of time and then charging to obtain the latentelectrostatic image as desired, respectively.

However, in employing this method it is observed that the sharpness of the image obtained is in some cases not satisfactory and that more specifically the boundary of the image is not clear but blurred so that image definition is poor. Although the cause of this deficiency is not quite understood it is believed that it may be due in part, to repulsion of the successive corona ions during charging due to the corona ions stored on the recording layer.

There is therefore a demonstrated need to provide improved electrophotographic imaging processes em ploying persistent conductivity imaging materials which produce images having good definition and sharpness.

It is therefore an object of this invention to provide an electrophotographic imaging system devoid of the above noted deficiencies.

Another object-of this invention is to provide an electrophotographic imaging system which employs a laser activating radiation in the exposure step.

Yet still another object of this invention is to provide a novel electrophotographic imaging method employing persistent conductivity materials.

Still another object of this invention is to provide a novel laser recording method employing persistent conductivity materials.

Yet still another object of this invention is to provide a novel electrophotographic imaging process employing laser beam activating radiation wherein exposure may be achieved in daylight conditions.

Yet still another object of this invention is to provide a novel eleetrophotographic imaging system employing laser radiation wherein a two-color image may be obtained.

These and other objects are accomplished in accordance with the system of the present invention generally speaking by, selectively activating a persistent conductivity material with laser irradiation and then charging and developing the material. For example, a suitable photoconductor such as zinc oxide dispersed in a resin layer is selectively exposed to laser radiation such as a helium neon (He-Ne) laser having suitable intensity of for example 5 lO w/cm The layer is then suitably charged for example with a corona ion charging device, and then conventionally developed employing for example, a cascade development system after which the visible image obtained may be fixed or otherwise employed.

The electrophotographic image of the instant inven tion may comprise any suitable photoconductive material possessing persistent conductivity. This material is normally provided in a photoconductive insulating layer over a base which is preferably conductive. The laser activating radiation may be employed in the dark or in daylight as desired, including the presence of artificial light as found in a normal indoor environment. The laser beam is irradiated onto the electrophotographic imaging material surface by employing any suitable technique including scanning the laser beam on the stationary material or by moving the material with respect to a fixed laser beam. After irradiation, the electrophotographic material is uniformly charged resulting in the surface of the member retaining charge in unexposed areas and having no charge in the exposed areas. The surface of the material bearing an electrostatic charge may then be developed employing a suitable toner either having the same polarity or an opposite polarity to that of the latent electrostatic image produced. Where the latent electrostatic image is of the same charge as that possessed by the toner used in development, non-image areas are developed. Where the latent electrostatic image is of opposite charge to that possessed by the toner employed in development, image areas are developed.

Any suitable inorganic or organic photoconductive material may be employed in the system of the instant invention which possesses persistent conductivity properties. Typical inorganic photoconductive materials include: sulfur, selenium, Zinc sulfide, zinc oxide, zinc cadmium sulfide, zinc magnesium oxide, cadmium selenide, zinc silicate, calcium-strontium sulfide, cadmium sulfide, indium trisulfide, gallium triselenide, arsenic disulfide, arsenic trisulfide, arsenic triselenide, antimony trisulfide, cadmium sulfoselenide and mixtures thereof. Typical organic photoeonductive materials include: triphenylamine; 2,4-bis( 4,4 '-diethylaminophenyl)-1,3,4-oxadiazol; N-isopropylcarbazole triphenylpyrrol; 4,5-diphenylimidazolidinone; 4.5-

diphenylimidazolidinethione; 4,5-bis-(4-aminophenyl)-imidazolidinone; 1,5-dicyanonaphthalenel 1,4- dicyanonaphthalene: aminophthalodinitrile; nitrophthalodinitrile: 1,2,5 ,o-tetraaza-N-isopropylcarbazole triphenylpyrrol; 4,5-diphenylimidazolidinone; 4,5- diphenylimidazolidinethione; 4,5-bis(4-aminophenyl)-imidazolidione; 1,5-dicyanonaphthalene; 1,4- dicyanonaphthalene; aminophthalodinitrile; nitrophthalodinitrilc; l,2,5,o-tetraazacyclocyclooctate-traene- (2,4,6,8 );2-mercapto-benzthiazole; 2-phenyl-4- diphenylidene-oxazolone; 6-hydroxy-2,3-di(pmethoxyphenyl)-benzofurane; 4-dimethyl-amino benzylidene-benzhydrazide; 3-benzylidene-aminocarbazole; polyvinyl carbazole; (2-nitrobenzylidene )-pbromo-aniline; 2,3-diphcnyl quinazoline; 1,2,4- triazine; l,5-diphenyl-3-methyl-pyrazoline; 2-( 4- dimethylaminophenyl )-benzoxazole; 3-aminocarbazole; phthalocyanines; -trinitro' fluorenonepolyvinylcarbazole charge transfer complexes and mixtures thereof. Of these zinc oxide and titanium dioxide dispersed in a suitable resin are pre ferred.

Any suitable resin may be employed with the photoconductive material of the instant invention. Typical resins include: thermoplastics including olefin polymers such as polyethylene and polypropylene; polymers derived from dienes such as polybutadiene, polyisobutylene, and polychloroprene; vinyl and vinylidene polymers such as polystyrene, styrene butylmethacrylate compolymers, styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene terpolymers, polymethyl-methacrylate, polyacrylates, polyvinylalcohol, polyvinylchloride, polyvinylcarbazolc, polyvinylethers, and polyvinyl ketoncs, fluorocarbon polymers such as polytetrafluoroethylene and polyvinylidene fluoride; heterochain thcrmoplastics such as polyamides, polyester, polyurethanes, polypeptides, casein, polyglycols, polysulfides, and polycarbonates; and cellulosic polymers such as regenerated cellulose, cellulose acetate and cellulose nitrate. Of these resins polyvinyl chloride, polyvinylidene chloride-polyvinylidene chloride copolymer, polyvinyl chloride-polyvinyl acetate copolymer, chlorinated polypropylene, chlorinated rubber, and copolymers of these with other polymeric materials are preferred.

Exposure to the laser activating radiation may be accomplished employing any suitable technique. For example, the laser radiation may be scanned onto the electrophotographic material which is stationary or the electrophotographic material may be moved with respect to a fixed laser beam.

Any suitable method of charging may be employed in the system of the instant invention. Typical methods of charging include: charge deposition resulting from air breakdown in the gap commonly referred to as TESI or charging in vacuo with an electron gun.

Any suitable method of development may be employed in the system of the instant invention. Typical methods of development include: cascade development, magnetic brush development, powder cloud development and liquid development.

Any suitable method of fixing may be employed in the system of the instant invention. Typical methods of fixing include: heat-pressure fusing, radiant fusing, combination radiant, conductive and convection fusing, cold pressure fixing and flash fusing.

In addition a two-color image may be obtained in employing the system of the instant invention by employing laser beams of varying intensities. For example, if a high enough intensity of laser irradiation is employed the photoeonductive material is blackened thereby rendering it visible and obviating the necessary development step. In the areas where sufficient laser energy has not impinged upon the photoeonductive surface so as to blacken the surface, these areas are rendered conductive during a subsequent charging and therefore may be developed with a toner material of a color other than black which has a charge the same as the electrostatic latent image obtained after such charging thereby producing a two-color image.

Any suitable laser beam in any suitable concentration may be employed to product the novel effects obtained in the system of the instant invention. High laser beam concentrations are required to obtain the effects achieved and preferably high concentrations or at least about lO /cm should be employed. Typical laser media include ruby, He-Ne, Argon ion, He or any other.

To further define the specifics of the present invention the following examples are intended to illustrate and not limit the particulars of the present system. Parts and percentages are by weight unless otherwise specified.

EXAMPLE I About parts by weight of zinc oxide is combined with about 400 parts by weight of methanol in which is dissolved 0.04 parts of eosine c.l 45380 and 0.06 parts of 3-carboxymethyl-5-[ (ethoxycarbonylmethyl-2- (3H)-thiazolidene) ethylidenel-rhodanine by dispersion with ultrasonic wave mixing. The supernatant liquid is removed after separation employing a centrifugal separator and about 200 parts by weight of N- butylacetate is added to the remainder and dispersed therein. The solution is centrifugally separated again and the slurry of zinc oxide with the absorbed dyes is obtained. About 12.5 parts by weight of styrenemodified alkyd resin, about 7.5 parts of polyisocyanate hardening compound, and N-butylacetate are added to 100 parts by weight of the above zinc oxide mixture the volume percentage of non-volatile matter being controlled to about 25%. This mixture is milled in a ball mill for about 6 hours resulting in a colored suspension. This suspension is coated on aluminum foil to a dry thickness of about 10 microns. After drying this coated layer is placed in an environment having a temperature of 40C for about 16 hours to completely cure the layer. The electrophotographic material thus prepared is irradiated in the dark with an argon ion laser beam having a Wave length of about 5145 A subsequent to dark adaptation. The laser has an output of 0.2 watts and the diameter of the laser beam employed is about 15 microns. The laser beam is emitted from a fixed laser beam generator and the electrophotographic material is placed around a drum which is rotated at a peripheral speed of about 4 meters per second. After irradiation by the laser beam the electrophotographic material is uniformly charged byvaconventional corona charging device to a negative polarity of about volts. The charged electrophotographic material is dipped in a developer solution prepared by suspending phthalocyanine green fine particles in kerosene. Phthalocyanine coloring material is attracted to the area radiated by the laser beam and a visible image is formed. The image thus formed possesses sharp lines of green on a background of magenta.

EXAMPLE II The process as outlined in Example I is again re peated with the exception that phthalocyanine blue is employed as the coloring material which deposits on the background or non-irradiated areas and develops the latent electrostatic image resulting in a sharp clean image.

EXAMPLE Ill The procedure as outlined in Example I is again repeated with the exception that the radiation of the laser beam is conducted at daylight (white light of 350 lux) after which the electrophotographic material is dipped into the kerosene suspension of phthalocyanine green subsequent to charging to the negative polarity resulting in the irradiated area being developed green.

EXAMPLE IV The procedure as outlined in Example I is again repeated with the exception that Brilliant blue F.C.F. (C.I. 42090) is employed as the dye material at 0.03 parts by weight. The electrophotographic material thus provided is exposed to a helium-laser beam having a wave length of 6328 A, with an output of SmW and a beam diameter of 30 microns traveling at a translational speed of 50 centimeters per second across the electrophotographic material. The material is then charged to a negative polarity as in Example I and dipped into a suspension of carbon black and kerosene. A black image is thus formed in the area irradiated by the laser beam. A large amount of lecithin is dissolved in the kerosene as a charge controller, the carbon black being charged to a negative polarity.

EXAMPLE V An electrophotographic material is prepared as in Example I and irradiated with a laser beam for 24 hours in the dark. The material is then uniformly charged in the dark and thereafter dipped into a kerosene suspension of phthalocyanine blue. The area irradiated by the laser beam is developed to a light density while the nonirradiatcd area is developed to a lower density.

EXAMPLE VI The procedure as outlined in Example V is again performed with the exception that the developing step is effected after charging and exposure to uniform white light resulting in development of only the laser irradiated areas.

EXAMPLE VII About 20 parts by weight of vinylchloridevinylacetate copolymer (weight ratio 70:30) and about 60 parts by weight of N-butylacetate are added to 100 parts by weight of zinc oxide and mixed together for about hours in a ball mill resulting in a white suspension. About 0.05 parts by weight of eosine dissolved in about 12 parts by weight of methyl alcohol are added to the suspension and stirred sufficiently to provide a colored suspension. The suspension is then diluted by N-butylacetate and coated on an aluminum foil paper to a dry thickness of about 10 microns. An argon-ion laser having an output of 0.6 watts and a wavelength of 5145 A and a beam diameter of about 50 microns is employed to irradiate this material in the daylight as in Example II at a scanning speed of about 20 cm/sec. thus resulting in the formation of black lines on the surface of the material. The laser beam is then reduced to an output of about 0.2 watts and the scanning speed is increased to about 4 m/sec so that blackening of the surface is eliminated. By charging and developing subsequent to irradiation as in Example II a green line is formed on the area having been irradiated by the laser beam. Thus a two-color image of black and green is obtained on the electrophotographic material.

Anyone skilled in the art will have other modifications occur to him based on the teachings of the present invention. These modifications are intended to be encompassed within the scope of this invention.

Although the present examples were specific in terms of conditions and materials used, any of the above listed typical materials may be substituted when suitable in the above examples with similar results. In addition to the steps used to carry out the process of the present invention, other steps or modifications may be used if desirable. In addition, other materials may be incorporated in the system of the present invention which will enhance, synergize or otherwise desirably affect the properties of the systems for their present use.

What is claimed is:

1. An electrophotographic imaging process comprising providing a photoconductive material having presistent conductivity properties such that after said material is irradiated with actinic radiation conductivity in the exposed areas temporarily persists, irradiating said material with a laser beam image-wise, uniformly charging said material and developing said material.

2. The method as defined in claim I wherein said laser is employed at an energy level not lower than l0 W-cm.

3. The method as defined in claim 1 wherein said photoconductive material is selected from the group consisting of zinc oxide and titanium dioxide.

4. The method as defined in claim 1 wherein said photoconductive material comprises a photoconductive material dispersed in a resin said resin being selected from the group consisting of polyvinylchloride, polyvinylidene chloride-polyvinylidene chloride copolymers, polyvinyl chloride polyvinylacetate copolymers, chlorinated polypropylene, and chlorinated rubber.

5. The process as defined in claim ll wherein said laser radiation is performed in the absence of light.

6. The process as defined in claim 1 wherein said irradiation is performed in daylight.

7. An electrophotographic imaging process comprising providing a photoconductive material having persistent photoconductivity properties such that after said material is exposed to actinic radiation the irradiated areas retain their conductivity, irradiating said material with a laser beam at a sufficient energy level so as to partially blacken the surface of said material imagewise, charging said material uniformly resulting in the formation of a latent electrostatic image on the surface thereof in the unblackened areas and developing said image by applying a non-black toner material having a charge opposite to the charge of said latent electrostatic image.

8. The process as defined in claim I wherein said laser is a helium-neon laser.

9. The process as defined in claim ll wherein said laser is a ruby laser. 

1. AN ELECTROPHOTOGRAPHIC IMAGING PROCESS COMPRISING PROVIDING A PHOTOCONDUCTIVE MATERIAL HAVING PERSISTENT CONDUCTIVITY PROPERTIES SUCH THAT AFTER SAID MATERIAL IS IRRADICATED WITH ACTINIC RADIATION CONDUCTIVITY IN THE EXPOSED AREAS TEMPORARILY PERSISTS, IRRADIATING SAID MATERIAL WITH A LESASER BEAM IMAGE-WISE, UNIFORMITY CHARGING SAID MATERIAL AND DEVELOPING SAID MATERIAL.
 2. The method as defined in claim 1 wherein said laser is employed at an energy level not lower than 102W-cm.
 3. The method as defined in claim 1 Wherein said photoconductive material is selected from the group consisting of zinc oxide and titanium dioxide.
 4. The method as defined in claim 1 wherein said photoconductive material comprises a photoconductive material dispersed in a resin said resin being selected from the group consisting of polyvinylchloride, polyvinylidene chloride-polyvinylidene chloride copolymers, polyvinyl chloride polyvinylacetate copolymers, chlorinated polypropylene, and chlorinated rubber.
 5. The process as defined in claim 1 wherein said laser radiation is performed in the absence of light.
 6. The process as defined in claim 1 wherein said irradiation is performed in daylight.
 7. An electrophotographic imaging process comprising providing a photoconductive material having persistent photoconductivity properties such that after said material is exposed to actinic radiation the irradiated areas retain their conductivity, irradiating said material with a laser beam at a sufficient energy level so as to partially blacken the surface of said material imagewise, charging said material uniformly resulting in the formation of a latent electrostatic image on the surface thereof in the unblackened areas and developing said image by applying a non-black toner material having a charge opposite to the charge of said latent electrostatic image.
 8. The process as defined in claim 1 wherein said laser is a helium-neon laser.
 9. The process as defined in claim 1 wherein said laser is a ruby laser. 